The OH radical disproportionates according to the elementary chemical reaction OH + OH H2O + O. This reaction

Question

The OH radical disproportionates according to the elementary chemical reaction OH + OH H2O + O. This reaction is second order in OH. The rate constant for the reaction is 2.0 x 10-12 cm3/molecule · s at room temperature. If the initial OH concentration is 1.0 x 1013 molecules/cm3, what is the first half-life for the reaction?

Answer 1

First half life = 1/(ka) = 1/(2x10^-12*10^13) s = 1/20 s = 0.05 s

Answer 2

reaction of Magnesium with Water(Steam) to provide Magnesium Hydroxide. i imagine you're wrong by technique of putting an arrow in the front of hydrogen somewhat than a plus signal. to operate to this the equation isn't even balanced